In a cave located in Lussac-les-Chateaux, France in 1937, two archeologists
were digging in a layer of Earth 15-20,000 years old. They had found and
removed some flint fragments for later inspection to see if they were the type
of prehistoric tools found in this strata, when they came upon some stones.
When they were brought out into the light they were found to have engravings
on them. Of modern people, wearing modern clothes. The stones (plural) are
in the Musée de l'Homme in Paris and are not on public display.

This drawing of one of the stones is from the Bulletin de la Société
Préhistorique de France.